The present invention relates to wireless communication systems, and more particularly, to a method and apparatus for efficiently communicating different types of control messages between a radio network and a mobile radio station.
In a typical cellular radio system, a geographical area is divided into cell areas served by base stations which are connected to a radio network. Each user (mobile subscriber) in the cellular radio system is provided with a portable, pocket, hand-held, or car mounted mobile station which communicates voice and/or data with the mobile network. Each base station includes a plurality of channel units including a transmitter, a receiver, and a controller and may be equipped with an omnidirectional antenna for transmitting equally in all directions or with directional antennas, each directional antenna serving a particular sector cell. Each mobile station also includes a transmitter, a receiver, a controller, and a user interface and is identified by a specific mobile station identifier. Each mobile subscriber is identified by another identifier, e.g., an international mobile subscription number (IMSI).
The growth of cellular radio telephone systems has compelled system designers to search for ways to increase capacity. One way to achieve this goal is to increase communications efficiency over the radio interface between the radio network and mobile radio stations. A large portion of the radio bandwidth available at this interface is allocated to carrying substantive traffic between mobile stations and the radio network. However, there is also a considerable amount of control information that must be transmitted between mobile stations and the radio network to perform various operations such as mobile registration, paging, call setup, handover, etc. Some of these operations occur quite frequently. Where possible, it is desirable to reduce the volume and frequency of such signaling to increase the amount of radio bandwidth available for substantive traffic, i.e., increased system capacity.
Besides a limited amount of radio bandwidth, another significant aspect of mobile radio communications is that batteries which power the mobile radio stations have a limited life before recharging is necessary. At least from a user""s perspective, the portability of mobile radios is enhanced as the size of those portable radios decreases. But smaller battery size typically results in shorter battery life. Accordingly, a desirable objective is to minimize the drain on a mobile""s battery while still providing reasonable access so the mobile radio can be quickly located by the radio network, e.g., in order to set up a call.
In traditional analog cellular systems, when a mobile station is idle, (not using a traffic channel), it tunes to and continuously monitors a control channel corresponding to its current cell in the network. As a result, the mobile can continuously determine whether a page message addressed to it has been received over a control channel. If so, the mobile then transmits a page response over the control channel to the base station which forwards the page response to the radio network. Upon receiving the page response, the radio network selects an available voice channel in the cell from which the page response was received and requests the base station in that cell to order the mobile station via the control channel to establish a through connection. Unfortunately, continuous monitoring of the control channel is a substantial drain on the mobile station battery.
In addition to control messages initiated by the radio network, e.g., pages, a mobile station may access the network to initiate a call by dialing the telephone number and pressing the xe2x80x9cSENDxe2x80x9d button on the telephone handset. A control signal including the mobile station identifier and the dialed telephone number is transmitted over the control channel to the base station and forwarded to the radio network which validates the mobile station, assigns a traffic channel, and establishes a through connection. If a mobile station moves between cells while a connection is established, a xe2x80x9chandoverxe2x80x9d of that connection takes place between the cells. Handover also requires control signaling over the radio interface.
In addition to call origination and page responses requiring the mobile to access the radio network using control signals, a mobile station often must access the radio network for purposes of location registration. For example, the mobile may periodically register with the radio network so that the network knows the cell, location area, or registration area in which the idle mobile station is currently located. In addition, the idle mobile station also preferably registers with a new cell each time it passes a cell or other area border.
As cellular systems have evolved, plural control channels have been used such as a general system broadcast channel (BCH), a paging channel (PCH), a reverse access channel (RACH) used by mobiles to access the radio network, and forward access channel (FACH) used by the base station to acknowledge mobile accesses over the RACH. In more sophisticated cellular systems, control signaling carried by control channels may be Time-Division Multiplexed (TDM) meaning that one or more mobile stations are assigned or associated with one timeslot in repeated frames of multiple timeslots. One benefit of this TDM approach is that during the other timeslots, an idle mobile station can enter a power savings or sleep mode to extend the life of the mobile""s battery. For example, mobile stations may be divided into different paging groups with each paging group being assigned a particular timeslot on a paging control channel. Rather than all mobiles listening to the paging channel for pages all of the time, an idle mobile station need only wake up from sleep mode and monitor the particular timeslot on the paging channel assigned to the paging group to which the mobile station belongs. The mobile station can xe2x80x9csleepxe2x80x9d during the other timeslots to save battery power. The amount of time the mobile spends reading paging messages and the time spent asleep represents a tradeoff between call setup delay and power consumption.
An example paging channel format with paging groups is shown in FIG. 1. The paging channel is divided into plural blocks 1, . . . , N. corresponding to successive timeslots in a frame. The paging blocks/timeslots are repeated in each successive frame. Paging groups i, i+1, i+2, . . . , i+Nxe2x88x921 may be assigned either statically or dynamically to a corresponding block. Each block corresponding to a paging group includes a page indicator field indicating whether a page currently exists for a mobile in that particular paging group along with a paging message which includes an identification of specific mobile(s) in the group being paged.
Current cellular systems are of the xe2x80x9cmultiple accessxe2x80x9d type and therefore must regulate access to limited communication resources by large numbers of mobile stations. As described earlier, mobile stations frequently require access to the radio network in order to register, respond to a page, originate a call, etc. It is therefore desirable to establish access restriction procedures that limit the number of mobiles and/or mobile types which are allowed to perform a particular access procedure, e.g., registration, call origination, etc. Without such restrictions, multiple collisions and large numbers of unsuccessful access attempts may occur. Such collisions, unsuccessful accesses, and successive access re-attempts result in inefficient use of the system and channel resources. Access restrictions may also specify a maximum number of access attempts in a particular time span for a particular mobile access group, a particular minimum mobile priority status or level of service, etc.
One manner for regulating mobile access to the radio communications network is now described in conjunction with an example, uplink random access channel (RACH) illustrated in FIG. 2. The random access channel is divided into multiple access slots 1, 2, . . . , i similar to slotted ALOHA. A mobile station may only transmit over the random access channel at a number of well defined time offsets, e.g., 1.25 millisecond offsets. The first access slot is aligned with the frame boundary of a downlink broadcast channel transmitted by the base station. These offsets help achieve orderly random access over a common channel potentially shared by many users. The radio network may restrict certain mobiles so that they are prevented from transmitting over any access slot on the random access channel for one or more types of access operations and/or for certain time periods.
In addition, specific restriction access parameters may be broadcast by the base station over a general broadcast channel. FIG. 3 shows a simplified example format of a broadcast channel which includes one or more initial identification fields identifying possibly the radio network, the particular operator, and the cell or base station. The broadcast channel may also include a field which indicates the number of current paging groups in the cell as well as the specific paging channel for that cell. Still further, the broadcast channel includes an access parameters field setting forth the current access restrictions being enforced in the cell. The broadcast message may also include other fields such as a supported cell services field, the output power at which the broadcast channel is being transmitted by the base station, identification of neighboring cells to be used in an idle mode, and fields containing other information which is not particularly relevant to the present invention.
FIG. 4 illustrates various example types of information that may be included in the access parameters field of the broadcast channel. One or more network access restriction parameters may be associated with different access groups of mobile stations, each mobile access group having its own identifier. In this example, the access parameters include a mobile group identifier field along with access restrictions such as a location/registration restriction, a call origination restriction, a peak bit transmission bit rate restriction, an initial power transmission restriction, and a peak power transmission restriction. Of course, one or more other restriction parameters may be employed. Moreover, other broadcasting formats may be employed, e.g., one or more access restriction groups are specified and then the restriction parameter(s) valid for the specified groups are broadcast only once or a few times.
FIG. 5 illustrates an example mobile access group restriction configuration. The mobile stations are assigned to one of eight access restriction groups. Attempts by mobile stations to access the radio network are controlled by restricting or outright prohibiting origination/location registration access messages from the mobile stations. In FIG. 5, access restriction groups 1 and 2 are restricted during a first restriction cycle interval, followed by groups 3 and 4, groups 5 and 6, and groups 7 and 8 being restricted in corresponding access restriction time intervals. After the restriction interval is completed for groups 7 and 8, the cycle repeats. The groups under restriction are changed periodically so as not to unfairly bias the restriction to certain access groups. This type of restriction information may be transmit in the access parameters field of the broadcast channel. During the time period an access group restriction is being enforced, any mobile stations belonging to the restricted access group which ignore the restriction and perform a call origination or location registration are detected, and further processes for those mobile stations are suspended. Presumably, most mobiles will comply with applicable restrictions. Of course, this is just an example, and different types of restrictions and restriction allocations could be employed.
The radio network therefore must frequently inform various mobile stations of changes in and the current status of the group of mobiles currently under restriction. Any time the radio network channel updates or otherwise changes the access parameters affecting one or more access restriction groups of mobile stations, the mobile stations in those groups must be specifically paged, and after receiving a page, tune to the broadcast channel so they can each decode the broadcast access parameters to become aware of the new network access restriction information. In current cellular systems, all mobiles in all access restriction groups must be paged since access restriction groups are not coordinated with mobile paging groups.
While such an approach to radio network access restriction is beneficial for controlling access to radio network services, it has a significant disadvantage. The mobile stations must be regularly paged specifically for the purpose of having the mobiles check the broadcast channel to obtain the current (and regularly changing) access restriction status information. Consequently, all of the mobile stations must regularly power-up out of sleep mode during all paging time slots to detect these pages which causes considerable drain on the mobile""s battery power. However, such pages are usually only relevant to a few of the mobile stations. What is needed is a way in which the mobile station can still regularly receive both paging information for the mobile or its paging group as well as access restriction information pertinent to that mobile or to its mobile access group relative to that mobile while at the same time conserve its battery power.
The present invention meets this need by coordinating paging, access restriction, and/or other network communications in a mobile telecommunications network. An example of another network communication is a request from the radio network sent to one or more mobiles requesting that those mobiles measure certain parameters, e.g., signal strength. The returned signal strength values may be used by the network for operations or maintenance tasks like system planning, etc. Indeed, the invention permits any set of activities that apply to one or more mobiles to be coordinated so that each such mobile need only power up once to receive all of the information related to that set of activities.
In one example, non-limiting embodiment, paging messages and network restriction messages are consolidated in one message. Paging groups of mobile stations and network access restriction groups of mobile stations are merged into a single set of paging and network access restriction groups to which different mobile stations belong. A mobile station therefore need only process one message in order to be informed about paging and network access restriction information pertinent to that mobile station. In this example, that one message corresponds to its consolidated paging and network access group, and the single paging and network access group message is transmitted during a specified time interval associated with the group. As a result, an idle mobile station belonging to that group need only leave a power savings sleep mode to receive that message during the specified group time interval. Otherwise, the idle mobile station can return to the power savings sleep mode to conserve its battery life.
An example method performed by a mobile station in accordance with the present invention includes the mobile station determining the time when it is to receive information transmit from the radio network. At that determined time, a message is received from the radio network, and the mobile determines if paging, access restriction, or other type of network information pertaining to that mobile is included in the message. If the mobile has been paged, it acknowledges the page. On the other hand, if the mobile has not been paged, it powers down to conserve battery life. If the mobile determines that the message contains an access restriction or other network message, it responds accordingly.
In the example paging and network access restriction embodiment, one or more nodes in the radio network establishes plural groups for mobile stations, each group being associated with one of plural specified time intervals. At a first time interval associated with a first one of the groups, the radio network node transmits a first message including information relating to paging and one or more radio network access restrictions pertaining to the first group of mobile stations. At a second time interval associated with a second one of the groups, the radio network node transmits a second message including information relating to paging and one or more radio network restrictions pertaining to the second group of mobile stations. The message may be a paging message transmit over an existing paging channel, and the first and second groups may correspond to first and second paging groups that also incorporate information corresponding to first and second network access restriction groups. The radio network node determines if a page exists to one of the mobile stations in the first (second) group, and if so, indicates in the first (second) message that a page should be read by the mobile stations in the first (second) group. In addition, the radio network node determines if a network access restriction exists for one or more mobile stations in the first (second) group and, if so, indicates the same in the first message.